Why Is Action Considered a Fundamental Concept in Physics?

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SUMMARY

Action is a fundamental concept in physics that serves as a cornerstone for various theories, including classical mechanics and string theory. It provides a unifying framework that extends beyond the Lagrangian and Hamiltonian formulations. The principle of least action allows physicists to derive equations of motion through the Euler-Lagrange equations, making it a powerful tool for analyzing physical systems. Understanding action enhances the ability to apply advanced theoretical concepts in physics.

PREREQUISITES
  • Classical mechanics principles
  • Understanding of Lagrangian mechanics
  • Familiarity with Hamiltonian mechanics
  • Basic knowledge of variational principles
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  • Study the principle of least action in detail
  • Explore the Euler-Lagrange equations and their applications
  • Investigate the role of action in string theory
  • Learn about variational calculus and its significance in physics
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Physics graduate students, theoretical physicists, and anyone interested in advanced mechanics and the foundations of physical theories.

robousy
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Hi all,

I'm a 2nd year physics grad student and have recently found this great forum.

I've taken a course on classical mechanics but never really appreciated why action is such a useful concept. I've noticed people talking about action a lot in things like string theory and it seems that action is more fundamental (?) or more useful (?) than simply the Lagrangian or the Hamiltonian but I do not see why.

If anyone could say a few words about why it is so useful to know the action ... and what you would then DO with it - then I would be very appreciative. (ie. what you can DO with the Lagrangian is stick it into the euler lagrange eqtns to get the eqtns of motion - what can you 'do' with the action).

Thanks in advance.

robousy
 
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This site says it better than I could: http://en.wikipedia.org/wiki/Action_(physics)

Admin edit: fixed link. I'm not sure why it was broken in the first place -- I might need to make sure the url parser vB code is working properly.
 
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